Flabelligera japonica Jimi, 2022

Jimi, Naoto, Hasegawa, Naohiro, Taru, Masanori, Oya, Yuki, Kohtsuka, Hisanori, Tsuchida, Shinji, Fujiwara, Yoshihiro & Woo, Sau Pinn, 2022, Five New Species of Flabelligera (Flabelligeridae: Annelida) from Japan, Species Diversity 27 (1), pp. 101-111 : 102

Flabelligera japonica Jimi , sp. nov.

[Japanese name: Kanten-habouki] ( Fig. 2 )

Material examined. Holotype (NSMT-Pol H-867): 8 mm in length, 1 mm in width, 38 chaetigers, complete body, Kominato , Kamogawa, Chiba, Japan (35°07′18″N, 140°11′02″E), 3 m depth, 26 July 2017, collected by Masanori Taru. Paratypes: 2 specimens (NSMT-Pol P-868), 8–9 mm in length, 1 mm in width, 36–38 chaetigers, complete body, collected with holotype; 5 specimens (NSMTPol P-869), 12–14 mm in length, 1–2 mm in width, 36–40 chaetigers, complete body, Hamamoroiso , Kanagawa, Japan (35°09′15″N, 139°36′28″E), 3–5 m depth, 13 December 2015, collected by Naoto Jimi, Masanori Taru, and Hisanori Kohtsuka .

Description. Body tapered posteriorly ( Fig. 2A ). Tunic thick, opaque, densely papillated, with cover of fine sediment particles. Chaetal lobes cover all of notochaetae and half of neurochaetae with sediment particles. Body papillae long, thin, digitate. Gonopodial lobes not seen.

Cephalic cage chaetae about 1/8 body length, as long as body width ( Fig. 2B ). Chaetiger 1 comprising cephalic cage; chaetiger 1 with 22 notochaetae and 15 neurochaetae per side. Chaetiger 1 longer than chaetigers 2–3. Chaetal transition from cephalic cage to body chaetae abrupt, chaetiger 2 with multiarticulated neurohooks.

Prostomium blunt cone. Brown eyes present, two pairs, anterior eyes larger than posterior ones ( Fig. 2C ). Caruncle developed, wide, exceeding branchial plate margin, distally truncate ( Fig. 2C ). Lateral lips developed, fused to dorsal lip ( Fig. 2C ). Ventral lip triangular, without ventral projection. Palps pale, thick, slightly longer than branchiae, about four times thicker than branchiae. Palp scars rounded, elevated. Branchiae in two lateral groups, each with filaments in concentric rows, each group with 18 filaments ( Fig. 2C ). Nephridial lobes paired, lateral to caruncle, at median distance of branchial groups.

Parapodia developed, lateral; median neuropodia ventrolateral. Notopodial lobes projected, digitate, truncate, covering half of notochaetae, without different papillae. Neuropodial lobes projected, digitate, without different papillae. Noto- and neuropodia widely separated. Notochaetae multiarticulated capillaries, transparent, 1/2 body width, 3 per bundle, with approximately 80 articles each; articles medium-sized distally, short medially and basally ( Fig. 2D–F ). Neurochaetae multiarticulated capillaries in chaetiger 1. Multiarticulate neurohooks present in chaetiger 2 and succeeding posterior chaetigers, golden, one per ramus, with 4–5 medium sized articles medially, other articles anchylosed, articles absent basally ( Fig. 2G, H ). Crest slightly wider than handle, width: length ratio 1: 5.

Posterior end truncated; pygidium with anus terminal, not covered by tunic, thick muscular ring, without anal cirri.

Etymology. The specific name is a Latinized adjective (japonicus, - a, - um), referring to the occurrence of the new species in Japan.

Remarks. This species resembles Flabelligera bophortica Annenkova-Chlopina, 1924 in having body without transverse bands, opaque tunic with fine sediments, one articulated neurohook per parapodia from chaetiger 2, long and golden crest of neurohook ( Annenkova-Chlopina 1924; Salazar-Vallejo 2012). The new species can be discriminated by the articulation of neurohooks. While articles of the new species neurohooks present medially, absent basally, and mostly anchylosed, articles in F. bophortica are long basally and short distally. Notopodial lobe of the new species exceed half of notochaetae, but not in F. bophortica .

As this species seems to be distributed in shallow subtidal areas in Honshu, the Japanese name “Kanten-habouki” is selected for this species. The species F. affinis has been considered as the sole Japanese Flabelligera species that are widely distributed in Japan ( Uchida 1992, 1994). This study shows that there is in fact no F. affinis present in Japan, but rather five species have been included in the “ F. affinis ” of Japan.

Figures

Fig. 2. Flabelligera japonica sp. nov., holotype (NSMT-Pol H-867). A, Whole body, lateral view; B, anterior end, lateral view; C, prostomium, frontal view; D, notochaetae, chaetiger 12; E, distal part of notochaetae; F, basal part of notochaetae; G, neurohook, chaetiger 12; H, middle part of neurohook. Scale bars: A, B, 1mm; C, 0.5mm; D, 200µm; E, F, 100µm; G, 200µm; H, 100µm. Abbreviations: bp, branchial plate; ca, caluncle; cc: cephalic cage; dL, dorsal lip; e, eye; ll, lateral lip; ps, palp scar.